Dealt with the same problem last winter and weatherstripping only helped so much. Ended up replacing the whole door and my heating costs dropped noticeably. The key is getting proper installation so there are no gaps. Found a local place that handles entry doors vancouver and they did solid work. I used them for entry doors vancouver installation and was very satisfied. They measured everything carefully and sealed it properly. If your door is more than fifteen years old replacement usually makes more sense than patching it up constantly